Desperate for advice on my 15 month olds separation anxiety

I’m at a loss guys! My back is against the wall, seriously. I’m a stay at home mom with 3 kids here and one on the way...my oldest two are 13 and 9 and I’m 36w1d pregnant. My youngest used to be really good about being laid in his crib with his bottle at bedtime and putting himself to sleep, but around the time he turned one he got a sick bug and my fiancé and I let him sleep in our bed for comfort for a couple nights and ever since then it’s been a nightmare, and getting WORSE! 😫 my fiancé works 12 hour shifts and leaves the house around 6am so obviously bedtime routine is on me....it’s to the point with my son won’t even PLAY anymore....if you set him in the floor with his toys he screams, if you put him in his bed he screams....I have no clue what to do anymore!!!! I’m gettin no sleep and I’m losing my sanity. I take him downstairs at bedtime usually for a snack so my man can sleep for awhile in hopes of tiring my son out...bring him uostairs, try his crib, that’s a no...try his cartoons, that’s a no...the only way he’s happy is in our bed and he’s usually still trying to sit up and play and climb. Right now at 11:30Am he’s currently standing by my bed screaming bloody murder because he wants to be up in the bed with me. I don’t understand.😭😭😭😭and yes I know he needs a routine but I don’t even know how to go about getting him back into one at this point. There’s still a ton of things I need to get done before this baby comes and I literally can’t get anything done unless I just let him scream it out in his bed. I can’t imagine going into labor on no sleep like I’ve been living on....I also can’t send him to my parents house like this while we are at the hospital for a day or two, I feel terrible. And lastly but most importantly how the hell are we gonna be able to deal with this when there’s a newborn to care for as well?! PLEASE, if anyone has any advice it would be greatly appreciated.